See linked thread/article in the signature are of my post here...it details exactly what you are asking about from Google and Android developers as to why Android works the way it does.
In order to help battery life, you can do what I do...which is whats posted below..this is what I do on my phone, and I continually got 14-17 hours out of my stock Droid X...YMMV...
1) Go into Settings--->Battery--->Nightime Saver Mode..this is actually IMO a better setting than Maximum Saver, at least on my Droid X.
2) Your e-mail accounts, do they sync on their own? What type of schedule? Sync only over WiFi or over 3G as well? Set them for WiFI Only if you are in a good WiFi area...extend the times out if you are mostly on 3G.
3) What type of signal reception do you have, Great, Good, Lousy or 2 Soup Cans and some String? If your signal reception is Low, your phone will work harder trying to stay connected and trying to bounce between stronger towers. If signal is really bad, but a free WiFi connection is available, switch the WiFi on and keep it on until you are in a better 3G area.
4) Do you have any Social Widgets, RSS Feed Widgets, Weather Widgets or any other Widgets/Apps that like to update themselves regularly? If so, what are the refresh times for each? Can you set them to only update on a Manual Push? If not, then set the frequency to the longest permissible time frame for your ease of use and lifestyle.
5) Set the Display Brightness to either Auto or the lowest setting that you can still see easily. That big juicy 4.3" screen is nice to look at, but it will usually be the largest battery hog on your phone...keep it in check as much as possible...
Thats basically all my "tricks" that I utilize to keep my Droid X going for upwards of 17-20 hours on any given day....I hope they might help you as well..."
